Rotary variable resistor



April 26, 1966 c. F. REMUS ROTARY VARIABLE RESISTOR Filed May 1, 1963INVENTOR.

CASIMER F. REMUS United States Patent 3,248,678 ROTARY VARIABLE RESISTORCasimer F. Remus, Tunkhannocir, Pa., assignor to The Bendix Corporation,South Montrose, Pa., a corporation of Delaware Filed May 1, 1963, Ser.No. 277,274 11 Claims. (Cl. 338164) This invention relates to electricalapparatus, and more particularly relates to a variable resistor. In theillustrative embodiment of apparatus in accordance with the invention,the variable resistor is specifically an hermetically sealedpotentiometer.

The invention has among its objects the provision of a novel variableresistor which fulfills all of the conventional requirements of suchdevices.

Another object of the present invention is to provide a novellyconstructed variable resistor or potentiometer which will obviate theoccurrence of errors between upscale and down-scale readings and errorsbetween input and output.

A further object resides in the provision of a novel variable resistorof the type wherein a movable contact engages an extended resistance ata selectively variable location therealong.

Another object of the invention resides in the provision of a variableresistor of such construction that the engagement between the movablecontact and the resistance minimizes wear imposed upon the resistanceand the contact.

Yet another object of the invention is the provision of a novel variableresistor wherein the zone of engagement between the resistance and thecontact is hermetically sealed from the atmosphere.

A still further object of the invention lies in the provision of avariable resistor wherein the relative motion between an extendedresistance and a contact movable therealong is such as to permit the useof fixedly connected flexible sealing means novelly combined withrelatively rotatable parts.

The above and further objects and novel features of the invention willmore fully appear from the following description when the same is readin connection with the accompanying drawings. stood, however, that thedrawings are for the purpose of illustration only, and are not intendedas a definition of the limits of the invention.

In the drawings, wherein like reference characters refer to like partsthroughout the several views,

FIG. 1 is a view in longitudinal section through a potentiometer made inaccordance with the invention, certain of the parts being shown inelevation and the section being taken on line 1-1 of FIG. 2;

FIG. 2 is a view in end elevation of the potentiometer of FIG. 1, theView being taken in a direction from left to right in FIG. 1, theresistance, the movable contact, and the connections between suchelements and the terminals of the potentiometer being shownschematically;

FIG. 3 is a view in transverse section through the potentiometer of FIG.1, the section being taken along the line 3-3 of FIG. 1; and

FIGS. 4 and 5 are detail views, partly in section, illustrating amodified form of wiper contact that may be used in the device of FIG. 1.

The apparatus of the invention is illustrated herein as an hermeticallysealed potentiometer, wherein the zone of engagement between an extendedresistance and a movable wiper contact is sealed from the atmosphere. Itis to be understood that the invention is not limited It is to -beexpressly under- ICC . the novel manner of adjusting the location ofengagement betweenthe movable contact and the extended resistance, areapplicable to variable resistors which need not be hermetically sealedand to other specifically different electrical devices, such asswitches.

Turning now to the drawing, the illustrative potentiom- I eter isgenerally designated by the reference character 10. Such potentiometerhas a circular cylindrical housing designated 11, such housing having acylindrical sidewall 12 made, for example, of metal such as steel. Thehousing 11 is completed by a rear end wall 14 and a forward end wall 15,both of such end walls being generally of disc shape. The end walls 14and 15 are secured and sealed to the peripheral wall 12 by annular welds16 and 17 therebetween, as shown in FIG. 1.

Disposed within the housing and spaced from the inner wall of housingpart 12 is an extended resistance 19 in the form of a helical ortoroidal winding supported on an .annular core 18 of suitableinsulation, such as ceramic,

or of metal covered with insulation. Resistance 19 and core 18 aresupported by having the forward annular edge thereof imbedded in andsealed to an annular mass 20 of potting compound, such annular massbeing located within and sealed to the wall of an annular recess 21 inan annular supporting member 22. Member 22 has an annular flange orpilot 24 extending forwardly from its forward Wall, flange 24telescoping within a rearwardly extending annular flange 25 on the rearface of the forward end closure member 15. One or more radiallyextending headed pins 26 are pressed into mating radial holes in flanges24 and 25 so as to secure the supporting member 22 and the resistanceassembly 19, 20 supported thereby in the position shown in FIG. 1.

A lead wire 27, connected to one end of the wound resistance 19, isconnected to a terminal 29 which extends through an insulating seal ofglass, ceramic or the like mounted in and sealed to the rear end closuremember 14 of the housing. The other .end of the wound resistance 19 isconnected by a lead wire 30 to a similar terminal 31, which is likewisemounted in a sealing insulator sealed to member 14 (FIG. 2):

If the resistance wire 19 is insulated, a central inner peripheral zoneof the winding is bated at an annular zone 33, indicated by phantomlines, so as to cooperate with a movable resilient wiper contact 32which is novelly mounted and so movable as to engage a selected part ofsuch zone 33 of the resistance. The movable contact 32 is of annularshape and is mounted upon an eccentric or crank means disposed on ashaft 34 mounted axially of the housing, whereby turning of the shaftprogressively changes the location of the point of engagement of thecontact with the resistance winding. Shaft 34 is rotatably mounted in ananti-friction bearing 35 mounted in the forward closure member 15 of thehousing and in a similar bearing 39 mounted inan annular support 40mounted on the rear closure member 14 of the housing. Bearing 35 isretained in a bore 36 in member 15 by means of a split spring ring 37which is snapped into an annular groove adjacent the forward end of bore36. Thesupporting member 40 for the rear bearing is of cup-like shape,such supporting member being accurately received within a centralcircular recess 41 in the inner wall of member 14 as shown.

The eccentric or crank on shaft 34 on which contact 32 is mounted isdesignated 42. Eccentric 42 preferably has an antifriction bearing 44mounted thereon as shown, the inner race of such bearing being carriedby the eccentric and the outer race of such bearing mounting contact 32through an interposed annular insulating member 46. The contact 32 maybe in the form of the rim of a wheel having a partially rolled orrounded rim 49 and a radially inwardly directed inner flange 47 which isimbedded in insulating member 46 or otherwise suitably mounted onhearing 44. Contact 32 is made of spring metal, such as berylliumcopper, whereby the rim or" the contact may resiliently yield somewhatas it engages resistance 19, thereby insuring secure electricalengagement between the contact and the resistance.

It will be seen that as the shaft 34 is rotated, as by a suitable knob(not shown) secured to the forward end of the shaft protruding from thehousing, the annular contact 32 moves bodily eccentrically with respectto shaft 32 without appreciable rotation upon its own axis so that theengagement between the contact and the resistance along zone 33 isprogressively changed. One revo- -lution of shaft 34 causes the contact32 to traverse the entire annular extent of zone 33 of the resistance,and thus causes the resistance between contact 32 and each of terminals29 and 31, to vary from a maximum to a minimum and viceversa,respectively. Thus, as the shaft rotates the contact has a combinedwiping and rolling engagement with the turns of winding 19. The contact32 has a hook-like terminal 50 thereon, terminal 50 being connected by aflexible lead wire 51 to a terminal 52 which is mounted in an insulatingbushing, such as a glass or ceramic seal, supported by and sealed to theend closure member 14. Wire 51 need only be sufficiently long to permitterminal 50 to move in a small circle having a diameter equal to thedifference between the diameter of shaft 34 and eccentric 42.

The space within housing 11 which includes the zone of engagementbetween the brush 32, 49 and the resistance 19 is hermetically sealedfrom the atmosphere, and may be filled, if desired, with an inert gas.In the illustrative embodiment, the sealing means includes a forwardflexible pleated metal sleeve or bellows 55 and a similar rear sleeve orbellows 56, the sleeves being sealed at the end-s thereof lyingintermediate the length of the housing to the annular contact supportingmember 45 and at their outer ends to the forward end closure member 15and the bearing supporting member 40. In order to effect such sealingconnections, the ends of the sleeves are bent over annular flanges onthe respective members to which the sleeves are attached and are brazedor welded thereto. Thus, the forward end closure 15 is provided with aninwardly extending annular flange 57 having a radially extending flange58 on its inner end. Member 45 has annular flanges 59 and 60, on itsopposite ends, and hearing supporting member 40 has a flange 61 on itsinner end for this purpose.

When the shaft 34 of the potentiometer is turned, in order to vary thelocation of the point of engagement between the contact 32 and theresistance 19, the flexible sleeves 55 and 56 are called upon to flexonly to a relatively small degree without rotation as the contactsupport 45 travels eccentrically. The bellows thus hold the Wipercontact assembly against rotation about its own axis when shaft 34 isrotated. It will be seen that the annular space within the housingoutwardly of sleeves 55 and 56 is thus sealed from the atmosphere, andthat no provision must be made for providing a seal at the forwardbearing 35.

In assembling the potentiometer of the invention, the sub-assemblycomprising the two bellows and parts 15, 40 and 45 is first made, thecontact 32 being already mounted on' ring 45. The sub-assemblycomprising members 18, 19, 26 and 22 is then mounted upon plate 15 toform a further, intermediate assembly. Bearings 39 and 44 are nextinstalled, followed by installation of shaft 34. The latter has annularflanges which position the bearings, the dimensions of the par-tspreferably being such as to pre-load the center bearing 44 and avoidbacklash or end shake. Bearing 35 is now put in place and locked inposition against a collar on the shaft by the split ring 37. After leads27, 3t and 51 are connected to their respective terminals on rear cover14, the cylindrical casing member 12 is slipped into position and weldedat 16 and 17. By providing additional bearing support in plate 15 forshaft 34, the left side of supporting member 45 could be closed and theleft end of the shaft with hearing 39 could be eliminated.

The end closure member 14 is provided with a hole 62 therethrough, suchhole communicating with the space within the housing lying radiallyoutwardly of sleeves 55 and 56. Such annular space to be sealed withinthe housing may be evacuated through hole 62, and any desired gaseousmedium introduced into the housing through such hole in a manner Wellknown to the art. A plug 64 may then be inserted into hole 62 and weldedto end closure member 14 in order finally to seal the space with in theenclosure or a tube may be mounted in said hole and then pinched closedand sealed when the casing has been backfilled.

In FIGS. 4 and 5 there is illustrated a modified form of annular wipercont-act which may be substituted for wiper contact 32, 49. As shown,said contact comprises a ring or annulus 66 made of resilient materialand a con tact or wiper ring 67 secured to the outer periphery thereof.Annulus 66 is preferably made of a high temperature spring material,such as Inconel, and comprises a disc-like portion 68 which may beembedded in insulating mass 46 and an axially directed flange portionhaving a plurality of slots 70 to form a series of spring fingers 69.The slots 70 between the fingers preferably extend somewhat into discportion 68. Contact ring 67 is secured by soldering or other suitablemeans to some or all of fingers 69. Ring 67 may thus engage resistance19 under resilient pressure the same as contact 32, 49.

The device of the invention is particularly characterized by itssimplicity, long life, and the ruggedness of its parts. The describednovel manner of mounting of the wiper contact, whereby the contact movesin a planetary manner within the resistance 19, distributes the wearingof the contact over its entire periphery, thereby insuring long,trouble-free operation of the contact. As the contact moves in suchmanner, it has both a rolling and wiping contact with the zone 33 of theresistance, whereby wearing of both the contact and the resistance isminimized while providing a satisfactory and desirable amount of slidingor wiping engagement.

Although only a limited number of embodiments of the invention have beenillustrated in the accompanying drawings and described in the foregoingspecification, it is to be expressly understood that changes may be madetherein. For example, neither the resistance winding assembly nor thewiper contact need form a complete annulus and shaft 34 need not berotatable through a complete revolution. If desired, the shaft may besupported at only one side of the wiper contact assembly, such as by apair of spaced bearings, and thus said assembly may be mounted at theend of the shaft, in which case the eccentric movement of the contactmay be realized by having the end portion of the shaft extend at anangle to the axis of rotation. In such modification, only one bellows orsealing sleeve is required and the contact supporting member forms asolid end closure therefor. If desired, a rigid wiper contact may beloosely mounted on insulating support 46 with an interposed resilientsupport, such as a split wavy leaf spring, to provide .the desirableresilient contacting force. Additionally, a series of circumferentiallyspaced contacts may be substituted for resistance 19 to provide a rotaryswitch. Various other changes such as in the relative dimensions of theparts, materials used, and the like, as well as in the suggested use ofthe apparatus of the invention, may also be made without departing fromthe spirit and scope of the invention as will now be apparent to thoseskilled in the art.

What is claimed is:

1. A variable resistor comprising an extended annular resistance member,a contact supporting member disposed within the resistance member,laterally flexible means for holding said contact supporting memberagainst rotation about its own axis, and arcuate contact mounted on theperiphery of the contact supporting member and tangentially resilientlyengaged with the inner peripheral surface of the resistance member, andeccentric means rotatable about the axis of the resistance member andfreely within said contact supporting member for oscillating the contactsupporting member and the contact relative to the axis of the resistancemember to vary the point of engagernent of said contact along saidresistance member.

2. A variable resistor as defined in claim 1, wherein the contact isresilient and circular in shape and has a relaxed diameter less than theinner diameter of the resistance member by slightly less than twice theeccentricity of said eccentric means, and the eccentric means for movingthe contact supporting member is an eccentric member journalling thecontact supporting member.

3. An hermatically sealed variable resistor comprising a gas impermeablesupport, an extended annular resistance member secured to the support, acontact supporting member arcuately movable along the resistanec member,an annular contact mounted on the contact supporting member andtangentially engaged with the inner periphery of the resistance member,means including at least a part of the support and flexible gasimpermeable diaphragm means connected to the support and the contactsupporting member for constantly sealing the zone of contact between theresistance member and the contact from the atmosphere, and eccentricmeans outwardly of the diaphragmmeans and rotatably journalled withinthe contact supporting member for moving the contact supporting memberand the contact carried thereby arcuately along the resistance member.

4. An hermetically sealed variable resistor comprising a housing havinga gas-impermeable peripheral wall, an

extended circular resistance member disposed within the housing andalong the wall of the housing, a contact supporting member arcuatelymovable along the resistance member, a contact mounted on the contactsupporting member and engaged with the resistance member, meansincluding the peripheral wall of the housing and flexible gasimpermeable diaphragm means connected to the housing and the contactsupporting member for constantly sealing the zone of contact between theresistance memher and the contact from the atmosphere, and eccentricmeans outwardly of the diaphragm means for arcuately moving the contactsupporting member and the contact carried thereby along the resistancemember.

5. An hermetically sealed variable resistor comprising a housing havingagas impermeable peripheral wall, an extended annular resistance memberdisposed within the housing, a contact supporting member disposed withinthe resistance member, a circular contact mounted on the contactsupporting member and tangentially engaged with the inner peripheralsurface of the resistance member, means including the peripheral wall ofthe housing and flexible impermeable diaphragm means connected to thehousing and the contact supporting member for sealing the zone ofengagement between the resistance member and the contact from theatmosphere and for holding the contact supporting member againstrotation about its own axis while permitting transverse movement of saidsupporting member, and means comprising an eccentric member journallingthe contact supporting member and rotatable about an axis coaxial withthe axis of the resistance member, said last-named means being outsideof the sealed space formed by theperipheral wall of the housing and thediaphragm means and radially within the resistance member for moving thecontact supporting member and the contact carried thereby along theresistance member, said contact having a relaxed diameter less than thediameter of the resistance member by slightly less than twice theeccentricity of said eccentric member.

6. An hermetically sealed variable resistor as defined in claim 5,wherein the diaphragm means is made up of two flexible generally alignedand circular cylindrical diaphragms, said diaphragms being sealinglyconnected at their outer ends to the peripheral wall of the housing andat theirinner ends to the contact supporting member.

7. A variable resistor comprising an extended annular resistance member,a contact supporting member dis- .posed within'the resistance member, acircular resilient contact rotatably mounted on the contact supportingmember within the resistance member, the rim of the contact beingtangent to and engaged with the inner peripheral surface of theresistance member at one zone of the resistance member, a shaft coaxialof the resistance member mounting the contact supporting membereccentrically with respect to the axis of the shaft, the contact havinga relaxed diameter less than the inner diameter of the resistance memberby slightly less than twice the eccentricity of said supporting member,and means for holding the contact against rotation about its own axiswhile permitting transverse movement of said supporting member, wherebyrotation of the shaft oscillates the contact relative to the axis of theshaft and causes the contact to roll along the inner peripheral surfaceof the resistance member.

8. Apparatus comprising a first member having a convex generally arcuatesurface, a second member having a concave generally arcuate surface insubstantially tangential engagement with said convex "surface, thelatter having a smaller radius of curvature than said concave surface,said second member including a toroidal winding of electrical resistancewire and said first member comprising an arcuate metallic contactresiliently engageable with said Winding, rotatable means having itsaxis of rotation concentric with said concave surface, means eccentricto and rotatable with said rotatable means for rotatably supporting saidfirst member, the difference between the radii of said arcuate surfacesbeing slightly less than the eccentricity of said eccentric means andmeans for holding said first member against rotary movement about itsown axis while permitting transverse movement of said first member.

9. Electrical apparatus comprising shaft means, support means forsupporting said shaft means for rotary move ment about a first axis,means eccentric to and rotatably movable with said shaft means, .acontact assembly mounted on said eccentric means to permit rotation ofthe latter relative to said assembly about a second axis movable aroundsaid first axis as the shaft means rotates, said assembly comprising aresilient electrical contact having an arcuate peripheral surfaceconcentric with said second axis, means for holding said assemblyagainst rotary movement about said second axis relative to said supportmeans while permitting transverse movement of said assembly, and meansincluding an electrical resistance having an arcuate surface concentricwith said first axis and tangentially engageable by the arcuateperipheral surface of said contact, the arcuate surface of thecontacthaving a radius less than the radius of said arcuate surfaceconcentric with the first axis by slightly less than the eccentricity ofsaid eccentric means, whereby said contact has combined rolling andsliding engagement with said last-named arcuate surface during rotationof said shaft means.

.10. Electrical apparatus comprising support means, shaft means havingcrank means and mounted for rotary movement on said support means, anannular electrical contact assembly comprising an annular metalliccontact mounted on said crank means to permit rotation of the latterrelative to the assembly, tubular means surrounding said shaft means andconnected to said assembly and to said support means, said tubular meansbeing flexible to permit movement of said assembly transversely of theaxis of said shaft means while holding said assembly against appreciablerotary movement about its axis on said crank means relative to saidsupport means, and an electrical resistance having a generally circularare concave surface concentric with the axis of said shaft means, saidcontact assembly including a generally circular arc convex surfaceresiliently engaging said concave surface.

11. A variable resistance comprising an extended circular arc resistanceelement, a contact supporting member mounted for rotation about the axisof the arcuate surface of the resistance element and having a circularportion eccentric to said axis, a resilient circulararc contact freelymounted on said eccentric portion of the supporting member with thearcuate surface thereof in face-to-face relation with the arcuatesurface of the resistance element, the radius of the arcuate surface ofsaid element being greater than the relaxed radius of the adjacentarcuate surface of said contact by slightly less than the eccentricityof said circular eccentric portion, whereby said arcuate surfaces havesubstantially tangential engagement, and laterally flexible means forholding said contact against angular movement about its own axis.

References Cited by the Examiner UNITED STATES PATENTS 1,569,042 1/1926Sheriff 338-168 X 1,731,003 10/1929 De Giovanni 338-154 X 2,007,4627/1935 Stoekle 338-202 X 2,041,380 5/1936 Stoekle 338-202 X 2,133,35810/1938 McCormack 74-18 X 2,293,407 8/ 1942 Schirrrneister 74-804 X2,457,814 1/1949 Gordy 338-154 2,497,867 2/1950 Cymmer 74-178 2,656,73710/1953 Lang 74-804 X 2,798,137 7/1957 Rasmussen 338-202 X 2,873,3392/1959 Bourns et al. 338-180 2,874,253 2/1959 Sharp et al. 338-1642,956,254 10/1960 Burns et a1. 338-162 3,067,396 12/1962 Carlstein338-154 3,081,022 3/1963 Miche 230-147 FOREIGN PATENTS 396,877 8/1933Great Britain. 813,467 5/ 1959 Great Britain.

RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Examiner.

3. AN HERMATICALLY SEALED VARIABLE RESISTOR COMPRISING A GAS IMPERMEABLESUPPORT, AN EXTENDED ANNULAR RESISTANCE MEMBER SECURED TO THE SUPPORT, ACONTACT SUPPORTING MEMBER ARCUATELY MOVABLE ALONG THE RESISTANCE MEMBER,AN ANNULAR CONTACT MOUNTED ON THE CONTACT SUPPORTING MEMBER ANDTANGENTIALLY ENGAGED WITH THE INNER PERIPHERY OF THE RESISTANCE MEMBER,MEANS INCLUDING AT LEAST A PART OF THE SUPPORT AND FLEXIBLE GASIMPERMEABLE DIAPHRAGM MEANS CONNECTED TO THE SUPPORT AND THE CONTACTSUPPORTING MEMBER FOR CONSTANTLY SEALING THE ZONE OF CONTACT BETWEEN THERESISTANCE MEMBER AND THE CONTACT FROM THE ATMOSPHERE, AND ECCENTRICMEANS OUTWARDLY OF THE DIAPHRAGM MEANS AND ROTATABLY JOURNALLED WITHINTHE CONTACT SUPPORTING MEMBER FOR MOVING THE CONTACT SUPPORTING MEMBERAND THE CONTACT CARRIED THEREBY ARCUATELY ALONG THE RESISTANCE MEMBER.